This invention is related to a sealing gasket and particularly to one adapted for use as a head gasket for motor vehicle internal combustion engines.
Conventional internal combustion engines for automotive applications require a head gasket between the engine block and the cylinder head for purposes of sealing against leakage of combustion gasses from the cylinder and, further to prevent leakage from cooling jacket passages and oil from the engine crankcase. While head gaskets have been used from the earliest days of internal combustion engines, designers of these gaskets are constantly striving to improve their performance, reliability, and reduce their costs. Present head gaskets are made from various materials such as a lamination of graphite foil facing material onto a tanged perforated steel core.
Although the newer gasket materials possess excellent sealing characteristics, gasket leakage remains a problem in certain areas of the head gasket. In V-type engines, the head gasket often includes a pair of extending "legs" extending at the ends of the gasket toward the centerline of the engine which are narrow extending surfaces where a seal must be provided between the cylinder head and block. If an effective seal is not provided in the leg areas, crankcase oil can leak outside the engine, giving rise to warranty claims, crankcase oil loss, and customer dissatisfaction.
Head gasket leakage in the leg areas is a particular concern in view of a number of factors. During the process of loading the cylinder head onto the engine block during production, the head is dropped into position, giving rise to areas of high gasket loading caused by the impact between the head and block. Due to the fact that the legs extend from the block such excess loading is particularly prevalent in the leg areas of the head gasket. The relatively small area of the leg portion means that the impact loads are necessarily concentrated. Composite gasket materials, like virtually any gasket material, have certain limitations in their ability to rebound after compression. In some instances, the impact encountered during cylinder head loading and installation are significant enough to prevent the gasket material from recovering to the degree necessary to provide sealing.
Another area of concern in the head gasket leg region is related to the fact that it is adjacent to the intake manifold sealing surface of the cylinder head. Typically, the cylinder head is first torqued to the engine block and thereafter the intake manifold is installed and torqued. Since the intake manifold is attached to both heads, the process of mounting the intake manifold can cause regions of the cylinder head to be lifted away from the head sealing surface on the sealing block. Further sealing problems arise due to thermal expansion of the intake manifold which often tends to lift the head from the block. Furthermore composite gasket material exhibit a mounting bolt clamp load loss over time, meaning that gasket clamping pressures are reduced, further reducing sealing effectiveness.
The previously mentioned sealing problems which exist when using conventional head gaskets are addressed by the gasket in accordance with the present invention. The gasket of this invention has a main body portion which can be virtually identical to existing head gaskets in shape and can be made of lamination of conventional gasket material such as graphite foil on a tanged perforated core. The present gasket, however, differs from prior art designs in that it features separate specially made sealing elements for the leg extension areas, preferably comprised of a perforated metal sheet which is attached to the main body of the head gasket. The extension seal carries a bead of elastomeric material such as silicone rubber. The extension seal can be attached to the main body of the head gasket through clenching type fasteners or various other fastening approaches.
The provision of the leg extension seal of this invention provides a number of significant benefits. Due to the structural characteristics of the rubber-like material employed, the extension acts as an energy absorbing "bumper" which serves to reduce the likelihood of over-compression of the head gasket due to impact between the cylinder head and engine block. Moreover, the elastomeric sealing bead serves to provide a seal capable of a high degree of compression and recovery for sealing against the leakage of crankcase oil or other fluids across the head gasket leg extension area.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.